Sometimes if you buy a drink in a glass bottle you can return that bottle and get some money back.
Let's assume we have "x" amount of money, the drink cost "p" per bottle, and we get "c" back money for each bottle.
If we have enough time, how much can we buy drinks for "x" money?
We have $10, drink costs $1, for each bottle we return we get $0.35
Step I: We buy 10 drinks We get $3.50 back for bottles
Step II: We buy 3 drinks and we are left with $0.50 We get back $1.05 back so we have $1.55
Step III: We buy 1 drink and we have $0.55 We get $0.35 for bottle, so we have $0.90 and we can't buy another drink for that.
Summary for $10 we were able to drink 14 bottles.